The present invention is related to a masonry cement having improved characteristics and reduced limestone content, utilizing materials such as kiln dust and fly ash, which would otherwise constitute waste products. More broadly, this invention relates to hydraulic cement mixes, for example hydraulic cement concretes, mortars, and grouts, neat cement mixes, non-plastic cement or concrete mixes, such as concrete block mixes, and dry mixes for making such concretes, mortars, and grouts.
A benefit of the present invention is the prevention of efflorescence, without impeding the curing of the cement, or adversely effecting the coloration thereof. Efflorescense, as encountered in concrete work, consists of the formation of hard accretions on the surface of the structure due to the leaching out of soluble materials from the interior of the structure by the escape of excess water therefrom, soluble materials thus translocated becoming carbonated on contact with the environment, and thus being rendered insoluble. In the construction of many types of structures, such as brick or block walls, water borne soluble salts, which are deposited on the concrete by the evaporation of water, produce the efflorescense in question. It has been suggested that evaporation of the water be entirely prevented, but this suggestion fails to solve the problem, since the liquid must be eliminated at some time to achieve setting of the cement, and whenever its escape is finally permitted, the dissolved salts will then be released and some provision must be made for controlling them, to the degree that efflorescence is eliminated.
Hydraulic cements are manufactured by mixing together in a finely divided state, in suitable proportions, either by a wet process or a dry process, suitable raw materials, usually of a calcareous and a siliceous nature, to produce compositions having hydraulic and cementitious properties. The mixed raw materials are heated together in a kiln, normally a rotary kiln, and burned at a temperature which causes sintering, or in some cases, they may be burned to actual fusion. After burning, the resulting product, usually called "clinker", is allowed to cool. In this stage of manufacture the cementitious compounds have been formed but exist in a physical state of relatively large pieces with very low surface area, in which form they cannot be used to make mortar or concrete mixes. This cement clinker is then reduced by grinding, usually in a ball mill of either the intermittent or continuous type, to a relatively fine state of subdivision having a relatively large surface area. During this stage, calcium sulfate in one form or another is normally added to the cement to prevent excessively rapid setting.
The hydraulic properties of a cement depend on its chemical compound composition and on the burning operation, but also to a considerable degree on the grinding and the extent of fineness to which it has been reduced. For example, the plastic properties and the rate at which the cement hydrates are markedly affected by the surface area, i.e., the degree of grinding. The grinding of cement clinker requires the use of considerable equipment, and consumes substantial time and energy. The grinding operation therefore adds substantially to the cost of manufacture of cement, and it will be obvious that lessening the extent of grinding would substantially reduce costs.
To be considered a good masonry mortar mix, a mix should possess a number of specific characteristics. For example, a mix must have a high degree of water retention and good workability and adhesion, as well as the ability to produce a mortar which adequately meets the strength requirements such as set forth by American Society for Testing and Materials (ASTM) or other recognized specifications.
Good water retention is one of the most important factors in an acceptable mix because of the desirability of retaining substantially all of the water in the mix before and during placement of the mortar so as to avoid premature stiffening. In mixes having poor water retention, there is a tendency for the mix to lose a high proportion or water by evaporation, bleeding, or absorption by porous surfaces coming in contact with the mix. For example, when a porous building unit is bedded in mortar, water will be absorbed into the porous structure thereof. The water lost in these situations frequently causes the mix to lose plasticity, which creates difficulties in the placement of such a unit. The mortar may also prematurely stiffen, which makes it difficult or impossible for a mason to make any changes in the position of the unit without breaking the adhesion between the placed unit and the mortar with which it is in contact. Adhesion and workability are also important properties of mortar mixes, since mixes possessing these properties can be easily applied (buttered) onto a brick or other building unit without dropping off or loss of a portion or all of the mortar before the brick can be positioned and tapped into its final location. The workability of a mortar mix also effects the speed and quality of workmanship of the mason doing the bricklaying. If a mix does not have good workability, the workman will have difficulty in buttering and properly positioning the brick, and as a result will lay fewer bricks in a given period of time. In addition, the lack of workability in a mix renders it exceedingly difficult for the workman to produce a strong and impervious joint.
While it is possible to prepare mortar mixes from cement, sand and water alone, the resulting mixes are harsh and crumbly and do not possess good working properties. In addition, the water retention of such mixes is undesirably low. As a result of these deficiencies, it has been customary to replace a portion of cement with a hydrated lime. This substitution improves workability and water retention, but creates other problems. The slaking or hydrating of the lime must be closely supervised to insure that hydration is thorough. Further, to achieve best results, the hydrated lime should first be mixed with water to form a putty, and the cement and sand mixed with the lime putty rather than using dry lime in the mix.
To eliminate the difficulties in the use of lime, additives have been incorporated in the cement during the manufacturing and bagging operations. The cements, commonly referred to as masonry cements, are prepared by intergrinding portland cement, a filler such as limestone, and an air entraining agent. The use of premixed masonry cements has become widespread due to the convenience of having the additives already incorporated before mixing, and due to the fact that mortars made therefrom frequently have improved water retention and workability as compared with most cement-sand mortar mixes and cement-lime-sand mortar mixes.
It is an object of the present invention to produce high strength mortar of improved workability and increased water retention while simultaneously eliminating the use of limestone as a filler.
It is another object of the invention to provide a process for increasing the strength of mortar without undue retardation of the rate of set and early strength. It is another object of the invention to provide a hydraulic cement mix having enhanced compressive strength and reduced water requirements for a given plasticity, together with an acceptable rate of set. It is a further object of this invention to provide a material of construction having essentially no efflorescence, and acceptable compressive strength and rate of set.
It is a further object of the invention to provide a means of utilization of kiln dust and fly ash, normally considered waste products. In this manner, the manufacture of cement is less energy intensive since it is blended rather than interground.
It is another object of this invention to provide an improved cement composition for use in grout or neat cement mixes, mortar mixes, or concrete mixes and similar mixes adapted for use as toppings, patches and other mixes where and high early strength is necessary or desirable.
Still another object of the invention is to provide hydraulic cement compositions comprising of cement, kiln dust and fly ash, either with or without aggregate material or ready mixes which can be dry-packaged and which provide, when mixed with water, setting times and early compressive strengths which adapt the compositions or ready mixes for use as a grout, mortar or concrete where high early strength development is necessary or desirable.
Other objects, features and advantages of this invention will become apparent from the following detailed descriptions which follow.